At both cellular and extracellular levels, cardiovascular and other diseases are characterized by the dynamic remodeling of the phospholipid-rich surfaces of lipid-based structures, like lipoproteins and cell membranes. This remodeling involves the generation in the surface of lipid metabolites, termed lipid second messengers, exemplified by diacylglycerols. Studies of one lipase that generates these metabolites have shown that their presence is a key requirement for the lipase to translocate from the surrounding aqueous medium to the surface where it functions. Moreover, lipase translocation requires a level of these lipid second messengers that exceeds a critical value. Below this value diacylglycerols are complexed with surface phospholipids and translocation is inhibited. We hypothesize that this regulatory mechanism is essential to the functions of not only lipases but many other, structurally-unrelated proteins that are crucial to cellular homeostasis and disease processes. The goal of this project is to test that hypothesis by determining the extent to which and mechanism by which diacylglycerol regulates the translocation of surface-seeking, independent folding units of selected proteins, i.e. domains, to and from highly controlled model lipid surfaces. Aim 1 studies determine how preexisting distribution of diacylglycerol and other lipid species in the surface regulates the ability of a domain to translocate to the surface. Aim 2 studies determine how lateral interaction of the domain and diacylglycerol within the surface regulates the time it spends at the surface. Aim 3 studies determine how the presence of one domain of a multi-domain protein residing in a surface can interact with diacylglycerol to produce a "self-assembled receptor" for effecting the translocation of another surface-seeking domain of that protein. The protein domains are parts of apolipoprotein E, munc 13-1 and pancreatic lipase and serve as models for a range of other biologically important proteins that share their domain motifs. Enabling these studies to be carried out is new methodology and unique new instrumentation developed for this project. The completion of this project will provide better understanding of the mechanisms by which diacylglycerols regulate essential biological processes, like cholesterol clearance (apolipoprotein E) and nerve transmission (munc 13-1). Moreover, results are expected to suggest strategies for regulating other processes which depend critically on the lipid surface organization.